Speed detection and control

ABSTRACT

A method of speed detection comprising the steps of recording pulse signals in a travelling tape or rotating body of magnetic material with an equal distance and reproducing the recorded pulse signals to detect the speed of the tape or the body. Speed control utilizing the above detection means comprises the step of comparing the phases of said reproduced pulse signals and a reference signal of a predetermined frequency to control the tape or body to move at a predetermined speed.

United States Patent Yano et al.

[451 May 30, 1972 [54] SPEED DETECTION AND CONTROL [72] Inventors:Osahiko Yano, Kadoma; Takahlro Nakamura, Neyagawa; Masahiro Deguchl,Yao, all of Japan [73] Assignee: Matsushita Electric Industrial Co.,Ltd.,

Osaka, Japan [22] Filed: Apr. 30, 1970 [21] Appl.No.: 33,265

179/1002 S; 340/174.1 A, 174.1 B

[5 6] References Cited UNITED STATES PATENTS 3,402,350 9/1968Shellabarger.. 1 79/1002 S 3,549,797 12/1970 Dann ..178/6.6 P 3,213,19310/1965 Konishi ..178/6.6 P

Primary Examiner-Howard W. Britton Attorney-Stevens, Davis, Miller &Mosher [57] ABSTRACT A method of speed detection comprising the steps ofrecording pulse signals in a travelling tape or rotating body ofmagnetic material with an equal distance and reproducing the recordedpulse signals to detect the speed of the tape or the body. Speed controlutilizing the above detection means comprises the step of comparing thephases of said reproduced pulse signals and a reference signal of apredetermined frequency to control the tape or body to move at apredetermined speed.

8 Claims, 8 Drawing Figures CW4 E5 l l W t .9 6

PULSE ASZZIBLE L M0701? AMP MUU/ AMP -24 SPEED F/L rm egg/mj g Q "PA/mm?--J Patented May 30, 1972 6 Sheets-Sheet 2 Patented May 30, 1972 6Sheets-Sheet V 5 l3? Qsmmk um Patented May 30, 1972 6 Sheets-Sheet 5Patented May 30, 1972 3,666,883

6 Sheets-Sheet 6 SPEED DETECTION AND CONTROL This invention relates to amethod of speed detection in which the running speed of a tape or therotation speed of a rotating body is derived as a signal of such afrequency which can represent the speed and to a method for controllingsaid tape or rotating body to a predetermined speed utilizing the abovespeed detection at the portion of a servo-circuit,

Among conventional techniques, there is a speed detection systemcomprising the steps of recording a reference timing signal of a certainfrequency additionally in the peripheral portion of a tapesimultaneously with the record of information and reproducing suchrecorded signal with the reproduction of recorded information to detectthe tape speed, and a speed control comprising the step of comparing thereproduced timing signal and the reference signal in the reproductionstep to control the capstan driving system.

According to the above method, however, the tape speed in thereproducing step cannot be accurately detected, even though the tapespeed in the reproducing step can be brought into coincidence with thetape speed in the recording step.

In other words, when there exists wow and flutter in the tape run in therecording step, the timing signals cannot be recorded with equalspacings in the tape so that the reproduced timing signals do notaccurately represent the tape speed at the reproduction step.

In case of a two rotating head type helical scan video tape recorder orthe like, video signals for one field are recorded as an oblique trackby a rotating head, regardless of the amount of wow in the tape supply.Thus, if there exists such wow in the recording step, there appear avariation in the relative speed with respect to the rotating head at aconstant speed and the video signal is recorded on the tape at a variedposition in accordance with the variations in the relative speed. In thecase of a capstan servo type tracking control system, reproduction iscarried out by detecting the rotation position signal from the shaft ofthe rotating head at a constant speed, reproducing the control signalrecorded in the recording step at the peripheral portion of the tape,comparing the phases of the two and controlling the speed of the tapesupply so that the rotating head accurately reproduces the informationrecorded as traces. When the control signal is recorded with variationsfrom the regular positions due to wow resulting from the tape drivingsystem in the recording step, the tape speed is controlled to reproducethe same situation as that in the recording step. There arises noproblem if such a control is perfectly performed, but, in the case ofcontrolling the speed of a rotating body having a certain inertia suchas a capstan, there appears a time lag in the servo system. In otherwords, there are usually present such frequency response characteristicsthat the servo system cannot accurately follow the frequency variations(due to tape wow) above a certain frequency (usually several Hz). Insuch cases, the reproduced signal derived from a rotating head isinevitably accompanied by time base errors in accordance with theresponse delay of the capstan servo system. In order to compensate forsuch variations, in high-fidelity VTRs, the structure for driving a tapeis made with higher precision to minimize the tape wow and a complicatedand expensive electric circuit is needed for compensating for thejittering components which cannot be compensated through a servo system.Although video tape recorders have been exemplified as exampleshereinbefore, in conventional high-fidelity tape recorders also, tapespeed wows are minimized by raising the accuracy of the mechanicalstructure to realize the same conditions in the reproducing step as thatof the recording step.

This invention is intended to solve the above problems.

An object of the invention is to provide an accurate speed detection byproviding a signal of such a frequency that truly represents the speedof a tape or the rotation speed of a rotating body regardless of the wowand flutter in the recording Step.

Another object of the invention is to provide a speed control utilizingsaid speed detection in a servo system for controlling a tape or arotating body at a predetermined speed.

A further object of the invention is to provide a tape speed controladapted for a rotating head type magnetic video reproducer.

Yet another object of the invention is to provide speed control adaptedfor a rotating disk type magnetic video reproducing apparatus using arotating magnetic disk.

According to an embodiment of the invention, there is provided a methodfor detecting the speed of a body of magnetic recording mediumcomprising the steps of bringing a first and a second magnetic head intocontact with a body of a magnetic recording medium at a predetermineddistance between the first and the second heads, said body being drivenby driving means and said first head being disposed before said secondhead with respect to the transfer of said body of recording medium,recording pulse signals of the output of an oscillator through saidfirst magnetic head, reproducing said recorded signals by said secondmagnetic head disposed after said first magnetic head, successivelyrecording pulse signals in said recording medium by synchronouslyoscillating said oscillator with said reproduced signals, and detectingthe transfer speed of said magnetic recording medium from the reproducedsignal of said pulse signals.

Description will now be made of preferred embodiments with reference tothe accompanying drawings in which:

FIG. 1 is a block diagram of the electric circuitry of an embodiment ofthe invention;

FIG. 2 shows the electric network of the main portion of the embodimentof FIG. 1;

FIG. 3 illustrates the operation of the embodiment of F IG.

FIG. 4 is a block diagram of the electric circuitry of an embodiment ofa rotating head type magnetic video reproducer apparatus according tothe invention;

FIGS. 5 and 6 are block diagrams of the electric circuitries of anotherembodiment of the invention;

FIG. 7 is a block diagram of an embodiment of a rotating disk typemagnetic video recorder according to the invention; and

FIG. 8 illustrates the operation of a conventional rotating disk typemagnetic video reproducer.

Similar reference numerals represent similar parts throughout thedrawings.

In FIG. 1, a magnetic tape 1 is driven by a capstan shaft 4 interlockedthrough coupling means 3 (not shown) or directly connected with acapstan motor 2, with, for example, a pinch roller pressed to andcooperating with the shaft 4. In the tape 1, there is provided a region5 for recording information and a track 6 for additionally recordingcontrol signals. Against the control track 6, a magnetic head assembly 7in which two heads 8 and 9 are molded with a predetermined gap pitch ispositioned. The two heads 8 and 9 are separated with a spacer 10 formagnetic shielding. The magnetic head assembly 7 is arranged to recordsignals of equal spacing in the tape. That is, the output 12 of anastable-multivibrator l l is recorded in the tape by the head 9 througha record amplifier 13. The multivibrator 11 has the property of beingsynchronized with and switched on by a pulse signal of a frequencyhigher than of its self-oscillation frequency. As the tape 1 proceeds onits way, the trace 14 of a pulse signal recorded by the head 9 passes bythe head 8 and at this moment the signal is reproduced (as indicated at15) and amplified by a pulse amplifier 16. The output of the amplifierl6 triggers the astable-multivibrator 1 1 to reverse the polarity. Then,the amplifier 13 amplifies the output of the multivibrator andre-performs the recording of a pulse signal through the head 9 to form atrace 17. Repeating these procedures, changes of magnetic patterncorresponding to the polarity reversal of the astable-multivibrator 11are recorded in the control track 6 of the tape 1 as is shown at 19, l8,14, 17, It is to be noted that with a suitable selection of the tapesupply speed, the gap pitch of the two heads and the self-oscillationfrequency of the astable-multivibrator 11, pulse signals are recorded inthe tape with a constant spacing determined by said pitch P regardlessof variations in the tape speed. That is, a reference signal can berecorded.

The reason for employing an astable-multivibrator (not, for example, aflip-flop or a monostable-multivibrator) is to enable successiverecordings of pulse signals even when the reproducing head 8 cannotreproduce the recorded signal by re-driving after being stopped or adrop-out of the tape, etc.

Assuming that the effective gap pitch P of the heads in P cm and thatthe predetermined tape speed is V cm/sec, the selfoscillation frequencyof the astable-multivibrator 111 should be set a little lower than V/2PHz I.

This allows for the oscilation to be synchronized with the reproducedsignal, even when the oscillation frequency is subjected to a change dueto fluctuations in tape speed, power source voltage, etc. In general,equation l may be represented as V/2P nI-Iz..... 2 where n is a positiveinteger or the inverse of a positive integer. In the cases of n y l, thereproduced signal for triggering the estable-multivibrator 11 may not bethe signal just previously recorded. For example, in the case of n 2, inthe reproduced signal (a leading and a trailing signal) only a leadingsignal is used for triggering the multivibrator.

FIG. 2 shows a detailed circuit network of an equally spaced signalrecording and reproducing circuit system used in the embodiment ofFIG. 1. The operation of the circuit of FIG. 2 will be apparent from thefigure for those skilled in the art.

Provided that V= 30 cm/sec and n 1, when the frequency of the reproducedsignal is desired to be set at 30 Hz, the effective gap pitch Pbetweenthe two heads becomes;

Thus, the astable-multivibrator 11 is set to have a self-oscillationfrequency a little lower than 30 Hz (at 28 Hz, for example). The signalof a square wave current of Hz is supplied to the recording head 9 toperform saturation recording in a magnetic tape. Positive and negativepulses are derived from the reproducing head 8 and are amplified andtheir polarity is reversed in the amplifier circuit. Then, the negativepulses 21 and 22 respectively triggers the two collectors of transistorsin the astable-multivibrator 11 to successively record the signal of 30Hz in the control track with equal spacing. FIG. 3 shows the waveformsof the astable-multivibrator of FIG. 2, in which letters t t and 2represent the time length of the recorded waveform and T indicates ahalf cycle of selfoscillation. The head assembly 7 should have such astructure so as to enhance the contact with a magnetic tape by means ofa pad, etc.

Control of capstan speed by equally spaced recorded signals will bedescribed hereinafter. In FIG. I, an external reference signal 23 of afrequency (for example 30 Hz) and the output signal 15 of thereproducing head having a frequency of 30 Hz or the output square wavesignal 12 of the astable-multivibrator 11 (in this case, the connectionis not shown) working as signal 24 to be compared with the referencesignal are supplied to a phase comparator 25 for comparison of theirphases. The phase difference between these signals 23 and 24 isfiltered, amplified and rectified at a low pass filter-amplifier circuit26 to apply a DC signal to a speed control circuit 27 for a DC motor 2for controlling the speed of the motor 2. Thus, the tape 1 is driven ata speed corresponding to the frequency of the external signal 23. Here,since the signal 24 represents the tape speed, wow and flutter resultingfrom the tape driving system have been compensated for.

For the method of employing a capstan servo, it is apparent that an ACsynchronous motor may be driven with the amplified output of a variablefrequency oscillator to control the variable oscillation frequency bythe phase difference component, or that an eddy current brake may beprovided to an AC induction motor so as to control the braking currentby said phase difference component.

Now, embodiments of a magnetic video recording and reproducing systemutilizing such a control system will be described referring to FIG. 4.

x 1:0.5 cm.

A rotating head disk 28 is provided with magnetic heads 29 and 30disposed with a spacing angle of to each other. With a 180 rotation ofthe disk 28, video signals of one field are recorded on and reproducedfrom a continuous oblique track 31. For example, a DC motor 2' iscontrolled to rotate at a speed of 1,800 rpm through a speed controlcircuit 27 by a 30 Hz signal 23 divided from the vertical synchronizingsignal of 60 Hz of the video signal and a rotation speed detectionsignal is derived from the assembly of permanent magnets 29 and 30disposed on the disk 28 and a stationary detection head. If thedetection signal is supplied one for each rotation of the disk, it willhave a frequency of about 30 Hz. As the synchronizing signal 23' and thedetection signal are supplied to a phase comparator 25 to compare theirphase and to apply the signal of their phase difference to the speedcontrol circuit 27' through a low pass filter-amplifier circuit 26' theDC motor 2' is arranged to be phase-synchronously driven by thesynchronizing signal 23. In recording process, switches 5,, S S and S,are set to R position and the synchronizing signal 23 (30 Hz) isrecorded in a control track 35 of a tape through a control head 34 toprepare a control signal 36 for use in tracking control in thereproduction process. Further, the capstan system is driven with highprecision by similar methods as stated before to minimize wow andflutter. A head assembly 7 detects the tape speed. In the recordingprocess, it can be cojointly used, for example, with the control track35. That is, if the head assembly 7 is positioned before the controlhead 34 with respect to the order of the tape transfer, equally spacedsignal traces after the detection of the tape speed are erased by thecontrol head 34 which performs saturation recording, thereby causing noproblem. Here, if the track width for the head assembly 7 is madenarrower than that of the control head 34, an advantage is provided inthat there occurs no risk of missing the erasing action.

In the reproduction process, switches S S S and 5 are connected to Pterminals, and a phase comparator 25 in the capstan servo system issupplied with the reproduced control signal which is recorded in therecording process and the rotation signal of the rotating head toachieve a tracking servo system. Here, it is apparent that a separatecontrol track may not be used if the head assembly 7 for detecting thetape speed is positioned before the erase head (not shown) with respectto the order of tape transfer.

Another embodiment is shown in FIG. 5. In the above embodiment of FIG.4, the tape speed is detected only in the recording process to minimizewow and flutter and not in the reproducing process connected with thetracking servo. In this embodiment, however, a control track 6 fordetecting the tape speed is' separately provided for both the recordingand reproducing processes to keep the tape speed constant. In this case,one comparison signal for a rotating head control loop is always usedfor the tape speed detection signal and the other comparison signal isthe output of a signal oscillator (30 Hz) 38 shaped by a pulse shaper39. Further, the oscillation frequency of the signal generator 38 ismade more stable if the generator 38 is composed of a buffer oscillatorwhich is triggered by synchronous signal pulses 23' to oscillatesynchronously.

Further, a practical magnetic video recording and reproducing system isshown in FIG. 6 in which, in comparison with the embodiment of FIG. 4,no separate control head (34 in the case of FIG. 4) is provided and theequally spaced signal traces 37 recorded for the capstan servo in therecording process are reproduced by the reproducing head 8 in areproduction process to form the control signal so as to perform thecapstan servo operation in synchronism with the external referencesignal 23'. Since the recording operation and the driving of a rotatinghead 28 are synchronously done in a particular phase relation with thereference signal 23', tracking of oblique record traces also becomespossible.

The structure of a head for detecting the tape speed has been describedto be a head assembly including two heads, but any other structure maybe adopted provided that the gap pitch between two heads can be set at apredetermined length.

Now, the invention will be further described in the case of a speedcontrol for a rotating body, or more concretely in the case of arotating disk type magnetic video recording and reproducing system.

In conventional rotating disk type magnetic video recording andreproducing systems, a magnetic sheet is rotated at a speed of 3,600 rpmin synchronism with the vertical synchronizing signal (60 Hz) oftelevision signals of the standard television signal code (60 fields,525 lines) to record the information of one field in one rotation.

Thus, horizontal synchronizing signals corresponding to lines arerecorded in one round. Therefore, on a magnetic sheet 101, as is shownin FIG. 8, horizontal synchronizing signals 103 are not recorded withperfectly equal spacing ofH, but a space of AH inevitably appears. In areproducing process, a disturbance appears in the horizontalsynchronizing signal at the position of said spacing of AH which isundesirable for providing a good reproduction of a stationary image in atelevision receiver.

This invention solves the above problem by rotating the magnetic sheetfaster or slower by an odd multiple of %H in every period of rotationthan by one-sixtieth seconds in synchronism with the verticalsynchronizing signal so as to record the horizontal synchronizingsignals equally spaced over the whole rotation.

Namely, one rotation of a magnetic sheet disk is brought intocorrespondence with 262, 263, etc times the horizontal synchronizingsignal period. For example, in the case of rotating a sheet disk incorrespondence with 262 times the horizontal synchronizing signalperiod, there is provided a detection signal of a rotation rate of 60 Hzin response to a rotation of for the magnetic sheet disk, where thevalue of 63.5 X represents a period of I H (seconds). And such adetection signal and a reference signal of 60 Hz are compared in theirphases. Then the rotation of the magnetic sheet is controlled accordingto the phase difference so as to synchronize with the reference signal.

In FIG. 7, a rotating disk 104 provided on a rotating shaft 105 issubjected to rotation control. A magnetic recording medium layer isprovided on the side or top surface of the disk 104. The rotating shaftis arranged to be rotated a little faster than a predetermined rotationspeed by a driving source through an elastic belt 106 when not undercontrol. A magnetic head 107 for recording pulse signals is brought intocontact with the recording medium layer of said rotating disk 104. Amagnetic head 108 is provided to reproduce record traces formed by saidrecording head 107. An astable-multivibrator 110 has a self-oscillationfrequency a little lower than the frequency of an external referencesignal (for example, vertical synchronizing signal of 60 Hz) applied toa terminal 111. The output of the astable-multivibrator 1 10 is appliedthrough a record amplifier 112 to said recording magnetic head 107 andsaturation-recorded in the recording medium. The output of thereproducing magnetic head 108 triggers the astablemultivibrator l 10through a reproduction amplifier 113 and is also fed to a phasecomparator 114 to be compared with the external reference signalthereat. The output of the phase comparator 114 representing the phasedifference is led through an amplifier 115 to an eddy current brake 116provided on the rotating shaft 105 to control the rotation of the shaft105. Provided that the disk 104 rotates in the direction shown by thearrow in this structure, if the reproducing magnetic head 108 ispositioned with an angle shift of 6 360/2625 toward the direction ofrotation from the position of 180 from the recording magnetic head withrespect to the rotation center of the disk, a rotating speed of for thedisk 101 will produce a signal of 60 Hz from the reproducing magnetichead.

As is described above, if the rotation detection signal (the output ofthe reproduction amplifier 113 or the output of theastable-multivibrator triggered by the output of the amplifier 113) andan external reference signal (the vertical synchronizing signal of 60 Hzapplied to the terminal 111) are compared in their phases to control theeddy current brake 116 by this phase difference, the disk 104 can besynchronously rotated at a speed of in particular relation to thevertical synchronizing signal.

In general, taking the frequency of the horizontal synchronizing signalas f Hz and the frequency of the vertical synchronizing signal as f, Hz,the rotation period of the disk can be arranged to be multiple times theperiod of the horizontal synchronizing signal if the rotation r (rpm) ofthe disk is set as where n is a positive or negative odd integer, fromthe equation of fin ers.

Provided that the gap arrangement of the two heads 107 and 108 has anangle A with respect to the rotation axis toward the rotating direction,detection of a rotation signal of a f where a is a positive integer orthe inverse of a positive integer, can be done by selecting A asfollows:

Further for controlling a rotating body to a rotation speed of r with anexternal reference signal of a frequency f Hz, the gap pitch A (degree)(with respect to the rotation center) of two magnetic heads on amagnetic disk for speed detection mounted on a rotating body is set tobe As is described above, for a constant reference signal and anarbitrary desired speed, a servo system which is kept in phasesynchronism with said reference signal can be formed by adjusting therelative position of the two heads and deriving such a speed detectionsignal that there is a particular relationship to the external referencesignal.

What is claimed is:

1. A method for controlling the transfer speed of a body of a magneticrecording medium driven by driving means comprising the steps ofbringing a first and a second magnetic head into contact with a body ofa magnetic recording medium at a predetermined distance between thefirst and the second heads, said body being driven by driving means andsaid first head being disposed before said second head with respect tothe transfer of said body of recording medium, recording pulse signalsof the output of an oscillator through said first magnetic head,reproducing said recorded signals by said second magnetic head disposedafter said first magnetic head, successively recording pulse signals insaid recording medium by synchronously oscillating said oscillator withsaid reproduced signals, comparing the phases of a signal related withsaid reproduced signals and an external reference signal to derive thephase difference signal and controlling said driving means with saidphase difference signal.

2. A method according to claim 1, in which said body of magneticrecording medium is a magnetic tape and said external reference signalis the horizontal synchronizing signal of the video signal to berecorded on said tape.

3. A method according to claim 1, in which said body of magneticrecording medium is a rotating magnetic disk.

4. A method for controlling the speed of a magnetic disk of a magneticdisk type magnetic video reproducer apparatus in recording video signalsfor one field of television signal according to an interlaced scanningsystem having a vertical synchronizing signal of frequency 1', Hz and ahorizontal synchronizing signal of frequency f Hz and a horizontalsynchronizing signal of frequency f Hz in a magnetic disk rotated bydriving means with a stationary head, comprising the steps of recordingthe oscillation output of an oscillator with a first magnetic head in arotating body of magnetic medium rotated in relation with said magneticdisk, reproducing the recorded signal of said output with a secondmagnetic head at a position spaced from said first magnetic head bydegree with respect to the rotation center of said rotating body ofmagnetic medium toward the rotating direction, synchronously drivingsaid oscillator with said reproduced signal, comparing the phases ofsaid reproduced signal and the vertical synchronizing signal reproducedby said second head to derive the signal of phase difference andcontrolling said driving means by said phase signal difference.

5. A method of controlling tape speed in a magnetic video recording andreproduction apparatus, comprising the steps of:

a. controlling a tape driving means during the recording of a televisionsignal, including the steps of:

driving a magnetic tape past first and second magnetic head means spacedapart a predetermined distance from each other,

recording output signals from a self-oscillator onto a recording trackof said magnetic tape through said first magnetic head means,

reproducing said recorded output signals from said magnetic tape by saidsecond magnetic head means,

triggering said self-oscillator with said signals reproduced by saidsecond magnetic head means,

comparing the phase of a signal relating to the vertical synchronizingsignal component of said television signal with the phase of the outputsignal of said selfoscillator by a first phase comparator, and

controlling said tape driving means by a signal corresponding to thephase difference obtained from said first phase comparator;

b. controlling a rotating head driving means during said recording,including the steps of:

recording a saturating control signal related to said verticalsynchronizing signal onto said recording track after said recordedoutput signals have been reproduced by said second magnetic head means,

comparing the phase of a signal corresponding to the rotation rate of arotating head with the phase of a signal relating to said verticalsynchronizing signal by a second phase comparator, and

controlling said rotating head driving means by a signal correspondingto the phase difference obtained from said second comparator; and

c. controlling said tape driving means during the reproduction of thetelevision signal recorded on said magnetic tape, including the stepsof: comparing the phase of said control signal with the phase of thesignal corresponding to the rotation rate of said rotating head by saidfirst phase comparator, and

controlling said tape driving means by a signal corresponding to thephase difference obtained from said first comparator.

6. A method of controlling tape speed in a magnetic video recording andreproducing apparatus, comprising the steps of:

a. controlling a tape driving means during the recording of a televisionsignal, including the steps of: driving a magnetic tape past first andsecond magnetic head means spaced apart a predetermined distance fromeach other,

recording output signals from a self-oscillator onto a recording trackof said magnetic tape through said first magnetic head means,

reproducing said recorded output signals from said magnetic tape by saidsecond magnetic head means,

triggering said self-oscillator with said signals reproduced by saidsecond magnetic head means,

comparing the phase of a signal relating to the vertical synchronizingsignal component of said television signal with the phase of the outputsignal of said selfoscillator by a first phase comparator, and

controlling said tape driving means by a signal corresponding to thephase difference obtained from said first phase comparator; b.controlling a rotating head driving means during the recording of saidtelevision signal, including the steps of: comparing the phase of asignal corresponding to the rotation rate of said rotating head drivingmeans with the phase of said signal relating to the verticalsynchronizing signal by a second phase comparator,

controlling said rotating head driving means by a signal correspondingto the phase difference obtained through said second phase comparator;and c. controlling said tape driving means during the reproduction ofthe television signal recorded on said magnetic tape, including thesteps of: comparing a signal corresponding to the output signal of saidself-oscillator and a signal corresponding to the rotating rate of saidrotating head, said output of said self-oscillator being related to thereproduced output of said second magnetic head means, and

controlling said tape driving means by a further signal corresponding tothe phase differences obtained from said first phase comparator.

7. A method of controlling tape speed in a magnetic video recording andreproducing system, comprising the steps of:

driving a magnetic recording medium past first and second magnetic headmeans spaced apart from each other a predetermined distance;

generating an output signal from an oscillator having thecharacteristics of an astable multi-vibrator;

applying said oscillator output signal to said magnetic recording mediumthrough said first magnetic head means;

reproducing said recorded output signal by said second magnetic headmeans;

applying said reproduced output signal to the input of said oscillator,thereby controlling the frequency of oscillation of said oscillator;

applying a signal corresponding to said reproduced output signal to aphase comparator;

applying, in a record mode, a signal corresponding to the verticalsynchronizing signal component of a television signal being recorded onsaid magnetic recording medium to said phase comparator;

applying the thus obtained first phase difference signal output of saidphase comparator to magnetic recording medium driving means; and

to control the speed of rotation thereof;

applying, in the reproduce mode of operation of said system, saiddetected phase of rotation signal and said signal corresponding to thereproduced output of said oscillator to said phase comparator;

applying the thus obtained second phase difference signal output of saidphase comparator to said magnetic recording medium driving means; and

controlling the speed at which said magnetic recording medium is drivenpast said first and second magnetic head means by said second phasedifference signal.

1. A method for controlling the transfer speed of a body of a magnetic recording medium driven by driving means comprising the steps of bringing a first and a second magnetic head into contact with a body of a magnetic recording medium at a predetermined distance between the first and the second heads, said body being driven by driving means and said first head being disposed before said second head with respect to the transfer of said body of recording medium, recording pulse signals of the output of an oscillator through said first magnetic head, reproducing said recorded signals by said second magnetic head disposed after said first magnetic head, successively recording pulse signals in said recording medium by synchronously oscillating said oscillator with said reproduced signals, comparing the phases of a signal related with said reproduced signals and an external reference signal to derive the phase difference signal and controlling said driving means with said phase difference signal.
 2. A method according to claim 1, in which said body of magnetic recording medium is a magnetic tape and said external reference signal is the horizontal synchronizing signal of the video signal to be recorded on said tape.
 3. A method according to claim 1, in which said body of magnetic recording medium is a rotating magnetic disk.
 4. A method for controlling the speed of a magnetic disk of a magnetic disk type magnetic video reproducer apparatus in recording video signals for one field of television signal according to an interlaced scanning system having a vertical synchronizing signal of frequency fv Hz and a horizontal synchronizing signal of frequency fH Hz and a horizontal synchronizing signal of frequency fH Hz in a magnetic disk rotated by driving means with a stationary head, comprising the steps of recording the oscillation output of an oscillator with a first magnetic head in a rotating body of magnetic medium rotated in relation with said magnetic disk, reproducing the recorded signal of said output with a second magnetic head at a position spaced from said first magnetic head by
 5. A method of controlling tape speed in a magnetic video recording and reproduction apparatus, comprising the steps of: a. controlling a tape driving means during the recording of a television signal, including the steps of: driving a magnetic tape past first and second magnetic head means spaced apart a predetermined distance from each other, recording output signals from a self-oscillator onto a recording track of said magnetic tape through said first magnetic head means, reproducing said recorded output signals from said magnetic tape by said second magnetic head means, triggering said self-oscillator with said signals reproduced By said second magnetic head means, comparing the phase of a signal relating to the vertical synchronizing signal component of said television signal with the phase of the output signal of said self-oscillator by a first phase comparator, and controlling said tape driving means by a signal corresponding to the phase difference obtained from said first phase comparator; b. controlling a rotating head driving means during said recording, including the steps of: recording a saturating control signal related to said vertical synchronizing signal onto said recording track after said recorded output signals have been reproduced by said second magnetic head means, comparing the phase of a signal corresponding to the rotation rate of a rotating head with the phase of a signal relating to said vertical synchronizing signal by a second phase comparator, and controlling said rotating head driving means by a signal corresponding to the phase difference obtained from said second comparator; and c. controlling said tape driving means during the reproduction of the television signal recorded on said magnetic tape, including the steps of: comparing the phase of said control signal with the phase of the signal corresponding to the rotation rate of said rotating head by said first phase comparator, and controlling said tape driving means by a signal corresponding to the phase difference obtained from said first comparator.
 6. A method of controlling tape speed in a magnetic video recording and reproducing apparatus, comprising the steps of: a. controlling a tape driving means during the recording of a television signal, including the steps of: driving a magnetic tape past first and second magnetic head means spaced apart a predetermined distance from each other, recording output signals from a self-oscillator onto a recording track of said magnetic tape through said first magnetic head means, reproducing said recorded output signals from said magnetic tape by said second magnetic head means, triggering said self-oscillator with said signals reproduced by said second magnetic head means, comparing the phase of a signal relating to the vertical synchronizing signal component of said television signal with the phase of the output signal of said self-oscillator by a first phase comparator, and controlling said tape driving means by a signal corresponding to the phase difference obtained from said first phase comparator; b. controlling a rotating head driving means during the recording of said television signal, including the steps of: comparing the phase of a signal corresponding to the rotation rate of said rotating head driving means with the phase of said signal relating to the vertical synchronizing signal by a second phase comparator, controlling said rotating head driving means by a signal corresponding to the phase difference obtained through said second phase comparator; and c. controlling said tape driving means during the reproduction of the television signal recorded on said magnetic tape, including the steps of: comparing a signal corresponding to the output signal of said self-oscillator and a signal corresponding to the rotating rate of said rotating head, said output of said self-oscillator being related to the reproduced output of said second magnetic head means, and controlling said tape driving means by a further signal corresponding to the phase differences obtained from said first phase comparator.
 7. A method of controlling tape speed in a magnetic video recording and reproducing system, comprising the steps of: driving a magnetic recording medium past first and second magnetic head means spaced apart from each other a predetermined distance; generating an output signal from an oscillator having the characteristics of an astable multi-vibrator; applying said oscillator output signal to said magnetic recording medium through said first magneTic head means; reproducing said recorded output signal by said second magnetic head means; applying said reproduced output signal to the input of said oscillator, thereby controlling the frequency of oscillation of said oscillator; applying a signal corresponding to said reproduced output signal to a phase comparator; applying, in a record mode, a signal corresponding to the vertical synchronizing signal component of a television signal being recorded on said magnetic recording medium to said phase comparator; applying the thus obtained first phase difference signal output of said phase comparator to magnetic recording medium driving means; and controlling the speed at which said magnetic recording medium is driven past said first and second magnetic head means by said first phase difference signal.
 8. The method according to claim 7, comprising the further steps of: detecting the phase of rotation of rotating magnetic head driving means; applying the signal corresponding to said detected phase of rotation and said vertical synchronizing signal component to a further phase comparator; applying the phase differences signal output of said further comparator to said rotating magnetic head driving means to control the speed of rotation thereof; applying, in the reproduce mode of operation of said system, said detected phase of rotation signal and said signal corresponding to the reproduced output of said oscillator to said phase comparator; applying the thus obtained second phase difference signal output of said phase comparator to said magnetic recording medium driving means; and controlling the speed at which said magnetic recording medium is driven past said first and second magnetic head means by said second phase difference signal. 